The Swans have lost two of their past three games, against Collingwood and Geelong, either side of a victory over 16th-placed St Kilda.
They have also added Dan Hannebery (knee) and Rhyce Shaw (knee) this week to an injury list that includes Adam Goodes, Sam Reid, Lewis Jetta and Lewis Roberts-Thomson.
The Swans are drifting in premiership betting, but Jack insists the Swans are still a force if they can recapture their best, starting with Hawthorn at ANZ Stadium on Friday night.
"We don't really worry about that. We've been written off before," Jack told reporters on Wednesday.
"We were probably written off at the back end of last year too.
"It doesn't worry us. Internally we know if we get right what we need to get right, we're more than capable."
The Swans could get some reinforcements this week, with Jetta and Roberts-Thomson both training well with the main group before the media was turned away from Wednesday's closed session.
A return through the reserves could also be an option if they prove their fitness, while Jack said Goodes was still hopeful of playing again this season despite another setback with his surgically repaired knee.
But Jack isn't sitting around waiting for help. He believes the youngsters who have been in the team all year and helped them back into the top four can do the job in the finals.
The co-captain also says last week's tough loss to the Cats will benefit the young Swans.
"That was probably one of the great things coming up against Geelong," he said.
"It gave a bit of a lesson to our younger boys of what's ahead, what to expect.
"Geelong are just a hardened side and it was a really valuable lesson for our boys coming into finals, absolutely.
"We've put ourselves in a position where we're fourth, we're still a good team and we can still compete with the best … but we have to make sure our whole 22 is accountable.
"Geelong absolutely smacked us in uncontested footy on the weekend, beat us in tackles, which is a sign of our hardness and our two-way spread, and that's something we pride ourselves on.
"We need to get that right and Friday night is a big chance for us to get back onto it."
Jack feels the Hawks, who comfortably cast aside the Swans at the MCG back in round seven, have been the benchmark side all season.
He also believes they could be susceptible to the Swans' outside run if the home side's midfield can get on top.
An anomaly of the draw means the two teams could meet twice in the next two weeks, this Friday and then again in a qualifying final.
And that holds no fears for the influential midfielder.
"It's certainly crossed our minds. It's probably a big possibility," Jack said.
"It is what it is. We're not worried about that.
"We're worried about this week getting right what we need to get right.
"Against Geelong we didn't get a lot of things right.
"That's our main focus, we get that right and then we move into finals, which is a different ball game altogether."
